What is the ruling on a man who divorced his wife while he thought she was not menstruating, but it turned out that she was menstruating?

Question : He divorced his wife while he thought she was not menstruating at the time of the divorce, but she turned out to be menstruating. Do we base the ruling on his belief, or do we base it on the reality?

Answer : We base it on the reality, and we base it on his belief only regarding the absence of sin. For example, he says, "I am not sinful," but the divorce does not take place according to the stronger position.